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For disease transmission it’s the average population density of the population not the country. Effectively the population density of each area * population in that area divided by total population. So, assuming 3 areas 1,000 square miles with 2,000 people, 100 square miles with 4,000 people and 10 square miles with 8,000 people you do :
(2,000^2/1,000 + 4,000^2/100 + 8,000^2/10) / (2,000 + 4,000 + 8,000) = 468.8 people per square mile, not (2,000 + 4,000 + 8,000) / (1,000 + 100 + 10) = 12.6 people per square mile. The reason is adding a huge area that nobody lived in (ex: 1 person across 1 million square miles) doesn’t change the calculation. (1^2/1,000,000 + 2,000^2/1,000 + 4,000^2/100 + 8,000^2/10) / (1+2,000 + 4,000 + 8,000) = 468.8 people per square mile |